The temporal pattern of appearance of hepatitis B surface antigen (HBsAg) in serum during acute hepatitis B has been well defined. However, quantification of HBsAg and its relationship to serum HBV DNA levels have not been studied. We quantitated HBsAg and HBV DNA in sera of individuals with acute hepatitis B who were followed prospectively. Levels and patterns of Hbsag and HBV-DNA were compared between patients who cleared Hbsag and those who progressed to chronicity. In the 12 individuals studied, 6 developed self limited, symptomatic acute hepatitis B, 3 developed mild acute disease followed by chronic hepatitis B, and 3 had silent seroconversion to antibody to hepatitis B surface antigen (anti-HBs) without symptoms or Hbsag. Hbsag was quantitated by RIA. Serum HBV-DNA was assayed by molecular hybridization and quantitated by scanning densitometry (sensitivity = 0.02 pg/sample). HBV-DNA was detected only in patients who were HBsAg positive for at least 1 month, appearing 7-20 (mean = 12) days after appearance of HBsAg. HBsAg was detectable sooner than HBV-DNA and persisted after HBV-DNA disappeared in the individuals with transient HBsAg. The onset and peaks of HBsAg and HBV-DNA occurred later in patients who became chronically infected. Levels of HBV-DNA correlated with levels of HBsAg (r=0.84, p=0.004) and highest values were noted in the 3 patients who developed chronic infection. These findings suggest that the development of chronic HBV infection is determined during the acute phase of infection and is characterized by high levels of HBV replication. Titers for hepatitis B e antigen (HBeAg) and its antibody (anti-HBe) were also estimated in these samples. Preliminary analysis of the data indicates that HBeAg and anti-HBe titers correlate with elevated HBsAg and HBV-DNA serum concentrations. Further analysis in regard to importance of the various markers for HBV in regard to the development of chronic infection is in progress. It is planned to test these sera for antibody to hepatitis C virus.